Block tester



BLOCK TESTER 2 Sheets-Sheet 1 Filed Feb. 18, 1965 INVENTORS Z mm E ZS UE K MR S H M HM M wm M mu. MW

ATTORNEYS United States Patent 3,323,359 BLOCK TESTER .lames K. Ely, Paramus, Paul D. Whyzmuzis, Clifton, and

William M. Gresenz, Rochelle Park, N.J., assignors to Interchemical Corporation, New York, N.Y., a corporation of Ohio Filed Feb. 18, 1965, Ser. No. 433,605 1 Claim. (Cl. 73-450) This invention relates to a device for measuring the blocking of materials, particularly plastic films, and more particularly to plastic films having printed matter thereon.

The term blocking, as applied to printed materials, is the rather strong adhension of a dried printed substrate in contact with another material, usually accompanied by some transfer of ink. The degree of blocking varies with the materials involved and with the temperature, pressure, time of contact, and humidity.

Standard block tests are usually made under pressures varying from 1 to 1000 psi, at temperatures of 100 to 180 F., and in relative humidity up to 100%. A common form of test is the determination of the degree of blocking after the stacked material has been subjected to a pressure of psi. overnight at 120 F. Humidity is sometimes controlled, but usually not.

The block tester of this invention consists essentially of 3 rigid plates, each having 3 holes equidistant from one another and preferably located near the periphery of the plate, forming the apexes of an equilateral triangle. The plates are mounted on 3 rods or posts, preferably threaded, passing through the holes, the posts then being parallel to one another and at right angles to the faces of the plates. Means are provided for clamping the lower plate firmly to prevent its sliding along the posts. In the middle of the lower surface of the middle plate is attached a rubber disk and another rubber disk of approximately the same circumference is attached to the middle of the upper surface of the lower plate. The circumferences of the disks approximately coincide when they are brought together by sliding the mounted middle plate down towards the mounted lower plate. A convenient size for the rubber disks is about 4 inch thick and 1 inch in diameter when the plates are about 2% inches in diameter. The size of the disks is not critical, but they should, naturally, not project over the edges of the plates nor interfere with the sliding of the middle plate on the posts.

The top plate and middle plate are separated by springs slipped onto the posts and located between the top plate and the middle plate. The springs are of approximately equal size and spring. The springs are preferably of such strength that the desired test pressure will produce almost 100% compression. Less compression may be used, but more accuracy in measurement is possible when compression is high. Means are supplied for clamping the upper plate so as to limit the distance it can he slid along the posts away from the other plates. The top plate, when not clamped, and the middle plate can move freely up and down, guided by the posts. The upper plate may be conveniently clamped, when the posts are threaded, by wing nuts on the posts. Usually bushings are helpful to reduce the number of turns required of the wing nuts. The lower plate may be clamped, when the posts are threaded, by nuts on the posts or the like.

The apparatus is set by putting the known weight desired on the top plate and then carefully clamping the plate in its resulting position by slipping the bushings over the posts and screwing on the wing nuts to hold the top plate in said position. The weight is then removed. The top plate cannot then move upward. The springs are under the desired tension. By measuring the distance between the upper plate and the middle plate, the apparatus ice may be manipulated with the top plate unclamped if desired. When it is to be used at the pressure for which it was calibrated, all that is necessary is to clamp the tcip plate again at the measured distance from the middle p ate.

Tests are carried out by placing the specimens between the rubber disks and clamping the upper plate in the position indicated by the calibrating weight to give the pressure desired. The whole apparatus is then put into a humidor jar containing some saturated salt solution and the jar is covered. The salt solution is selected to impart the desired humidity to the air in the jar. Such solutions are known to the art. The block tester is preferably made of such size that it may be readily put in a quart jar with enough headspace left to permit covering the jar tightly. The jar is heated, for instance in an oven, for the period of time, and at the temperature desired. The test specimen is then removed, cooled to room temperature and inspected to determine the degree of blocking. When the specimen is originally inserted in the block tester, its edges should project out beyond the region compressed by the rubber disks. The projecting, no pressure areas will occasionally show blocking; however, this type of blocking is not as consistently reproducible as that in the compressed area. When rigid disks are used instead of rubber ones, the test results are far less reproducible than those obtained with rubber disks. The preferred shape of the rubber is disklike, but the precise shape is not critical.

One form of embodiment of this invention is shown in the drawings where FIG. 1 is an exploded view of the elements that make up the apparatus, the lower plate already being clamped.

FIG. 2 is a perspective view of the a paratus being calibrated with a known weight, the bushings and wing nuts for clamping the upper plate being in place.

FIG. 3 is a cross-sectional view of the apparatus in the jar 22 containing the salt solution 26 for establishing the required humidity. It illustrates in particular a method for preconditioning the sample 25 without exertion of pressure, and subsequent application of pressure without removal from the jar. The middle plate is here held away from the sample by props, which are the hollow cylinders 24, 24.

FIG. 4 is a cross-sectional view of the apparatus assembled and placed in a humidor jar.

In the figures 10 is the lower plate,

11 is the middle plate,

12 is the upper plate,

13 is the lower rubber disk,

14 is the upper rubber-disk,

15, 15, 15 are threaded posts,

16, 16, 16 are springs,

17, 17, 17 are bushings,

18, 18, 18 are wing nuts,

19, 19, 19 are nuts,

20 is a known weight, and

21, 21, 2.1 are holes in the plate,

22 is a jar with a removable cap,

23 is a rod for manipulating the props,

24, 24 are props in the form of hollow cylinders,

25 is the sample to be tested,

26 is the salt solution for establishing the required humidity.

To apply pressure, the operator inserts a rod 23, as shown in the figure and pries out the props, whereup the middle plate is driven down on the sample by the springs. Here obviously extreme compression could not be used; however, there appear to be few occasions when pm-conditioning of the sample will be of interest. Metal parts are best made of corrosion-resistant material because of the exposure to salt solutions, for instance stainless steel is effective. The plates, besides being made of metal, can be made of rigid plastic instead, such as polystyrene, polymethylmethacrylates, etc., the plastics being less expensive than suitable metals.

The relative humidity of the air at 100 F. over saturated salt solutions at equilibrium is 77% for NaCl,

96% for K 50 53.5% for Na Cr O and 30% for MgCl .6-H O.

What is claimed is:

A block tester consisting essentially of (a) 3 rigid plates, each having 3 holes equidistant from one another, I

(b) 3 posts passing through the holes in the plates and thereby being parallel to one another and at right angles to the faces of the plates,

(c) means for clamping the lower plate in a fixed posi tion relative to the posts,

(d) means for clamping the upper plate in a fixed position relative to movement away from the lower plate,

(e) 3 springs of approximately equal size and spring, each being coiled around a separate one of said posts between the upper plate and the middle plate,

(f) a rubber disk attached to the middle of the lower surface of the middle plate,

(g) a rubber disk attached to the middle of the upper surface of the lower plate,

(h) the disks being of approximately the same circumference and their circumferences approximately coinsiding when brought together by sliding the middle plate along the posts.

References Cited UNITED STATES PATENTS 1,979,267 11/1934 Howe 73-15O X 2,691,886 10/1954 Cole 7394 20 LOUIS R. PRINCE, Primary Examiner.

S. C. SWISHER, Assistant Examiner. 

